Meningeal Solitary Fibrous Tumors with Delayed Extracranial Metastasis

Abstract

Background: The term solitary fibrous tumor (SFT) is preferred over meningeal hemangiopericytoma (HPC), because NAB2-STAT6 gene fusion has been observed in both intracranial and extracranial HPCs. HPCs are now considered cellular variants of SFTs.

Methods: This study analyzes 19 patients with STAT6-confirmed SFTs, who were followed for over 11 years in a single institution. Ten patients (10/19, 56.2%) had extracranial metastases (metastatic group), while the remainder (9/19) did not (non-metastatic group). These two groups were compared clinicopathologically.

Results: In the metastatic group, the primary metastatic sites were the lungs (n = 6), bone (n = 4), and liver (n = 3). There was a mean lag time of 14.2 years between the diagnosis of the initial meningeal tumor to that of systemic metastasis. The median age at initial tumor onset was 37.1 years in the metastatic group and 52.5 in the non-metastatic group. The 10-year survival rates of the metastatic- and non-metastatic groups were 100% and 33%, respectively. The significant prognostic factors for poor outcomes on univariate analysis included advanced age (≥45 years) and large initial tumor size (≥5 cm). In contrast, the patients with higher tumor grade, high mitotic rate (≥5/10 high-power fields), high Ki-67 index (≥5%), and the presence of necrosis or CD34 positivity showed tendency of poor prognosis but these parameters were not statistically significant poor prognostic markers.

Conclusions: Among patients with SFTs, younger patients (<45 years) experienced longer survival times and paradoxically had more frequent extracranial metastases after long latent periods than did older patients. Therefore, young patients with SFTs require careful surveillance and follow-up for early detection of systemic metastases.

Keywords: Central nervous system; Hemangiopericytoma; NAB2-STAT6 gene fusion; Neoplasm metastases; Solitary fibrous tumors.

Fig. 1.

Representative brain magnetic resonance images and histopathology of the primary brain tumor from case 10. (A) Prior to radiation therapy. A large, solid and cystic mass is observed in the right frontoparietal lobe with strong enhancement. There was severe mass effect. Intratumoral vessels were identified. (B) After preoperative radiation therapy. The tumor decreased in the size after radiation therapy. (C) The tumor demonstrates low cellular and edematous areas with staghorn-shaped vasculature. The tumor cells may have been ablated by radiotherapy. (D) Aberrant STAT6 nuclear positivity is observed in the primary brain tumor.

Fig. 2.

Computed tomography (CT) and pathology of a metastatic solitary fibrous tumor from case 10. (A) Liver CT scan showing a large, 12-cm soft tissue mass in the right lobe with prominent feeding vessels. (B) The cut surface of a hepatic tumor specimen showing a well-circumscribed, yellowish-tan-colored, solid tumor with multifocal necrosis, and hemorrhage with dilated vessels. (C) Microscopic examination of the liver mass reveals small, discohesive tumor cells with oval nuclei and fine chromatin. Staghorn-shaped hyalinized vessels and osteoclast-like multinucleated giant cells are identified. (D) Tumor cells are focally positive for CD34 on immunohistochemical staining. (E) Aberrant STAT6 nuclear positivity is observed in the metastatic tumor cells in the liver. (F) Ultrastructurally, the tumor is composed of sheets of oval to elongate cells around small capillaries. The tumor cells have nuclei with an oval or indented appearance, and fine, granular chromatin. Skein-like nuclei are also present. The individual tumor cells are surrounded by a thick, electron-dense, amorphous, external laminar material (arrowheads; uranyl acetate and lead citrate, × 5,000).

Fig. 3.

Kaplan-Meier survival curves of patients with solitary fibrous tumors according to the presence or absence of systemic metastases. (A) Paradoxically, the patients with systemic metastases had better prognosis than did those without metastasis. Metastases usually arose approximately 10 years after the initial tumor development. Therefore, only longer survivors developed systemic metastases. (B) Younger patients lived longer and had better survival. The age cut-off to demonstrate a meaningful survival difference is 45 years. (C) Patients with an initial tumor size > 5 cm have poorer survival than did those with smaller tumors. (D) The age of tumor onset is significantly younger in patients with systemic metastases than it is in patients without metastases. The median ages of onset in patients with and without systemic metastases are 37.1 years and 52.5 years, respectively.